It is estimated one out of ten Americans suffer from conductive as well as sensorineural hearing loss. While conventional hearing aids can offer moderate rehabilitation, inherent limitations, such as ear canal irritations, distortion and occasional ringing, and social problem with being perceived as handicapped have deprived many patients of clear hearing. Partially implantable cochlear and middle ear hearing aid systems can enable people with severe hearing loss to gain improved hearing and speech function. However, the external microphone and electronics present concerns on reliability, comfort, inconvenience, and social stigma.
Implantable microphones can be coupled to middle ear bones. For example, piezoelectric material can be used to sense the malleus vibration. However, piezoelectric material is generally stiff and it is therefore difficult to maintain precise contact with middle ear bones. Electro-magnetic sensors can similarly be mounted on middle ear bones, but present large loading effects that affect sound quality, and have the added disadvantage that they prevent the person from ever getting an MRI. Other microphones are implanted under the skin. However, these microphones tend to pick up body noises, such as chewing, through bone conduction or conduction through body tissues. As a result, most existing semi-implantable middle ear hearing systems and cochlear prosthesis use external microphones.